Electrical transmission or reproduction of sound



Nov. 3,1925. 1,559,847

s. (5. BROWN ELECTRICAL TRANSMISSION OR REPRODUCTION OF SOUND.

Filed May 29, 1922;

\ OYO.HOMA

Patented Nov. 3 1925.

UNITL Z Ma .t.

SIDNEY GEORGE BROXVN, 01 NORTH ACTON, ENGLAND.

ELECTRICAL TRANSMISSION Application filed May 29,

To all whom ii: may concern Be it known that" I. SIDNEY 'Gnouun Brown, a subject of the King of Great. Britain, residing at Victoria Road, \i illesden' Lane, North Acton, in the'connty oi Mid dlesex, England, have invented certain new. and useful lmprovements in the Electrical Transmissionor Reproduction of Sound. of which the following is a specification.

This invention relates to .the electrical transmission or reproduction of sound for telephonic purposes or for u se.with a grainophone, phonograph or like sound recording instrument. One object ot the invention is to obtain a reproduction of the sound in a loud tone which can be heard over a cong side'rable distance and is free from the disturbances usually accompanying sound re; production.

A further object is to conduct away rapidly the heat generated in a microphone utilizing substantial currents so as to prcvent disturbances due to an excessive rise in temperature. A still further object is to-provide in a. microphone built up of massive parts for easy and eilicient filling: of the microphone ,chambers with the microphone granules.

In order that the said invention may be clearly understood and readily carried into effect, the same will now be described n'iore *lully with reference to the accompanying drawings, in which Figure 1 is a' Section of a microphone de vice embodying this invention.

Figure 2 is a part front elevation and l igure 3 a back view of the same device.

Figure 4 is a detail view to a larger scale showingthe connection between a pair of microphone plates.

Figure 5 is a diagram of a transformer circuitembodying one feature of this invention, and

li 'ures 6, 7 and S are diagrammatic views showing an arrangement of microphones as fitted to a gramophone. I

The: left uppercorner of Figure 1 between the lines 00 00 is a section on the line'y-y of Figure 3, while the remainder of Figure 1 is 'a central section on the line .-2 Figure. I: The low'er half of Figure 2 is a front. elevation otthe device while the upper halt shows the front part removed to expose the discs of which the. casing is built.

Retort-in to the construction ot the ini- \l laws in l itrures 3. to 4%.. the hodv The discs It 01?. REPRODUCTION OF SOUND.

1922. Serial No. 564,386.

of the microphone. is built up in the form ot a substantial metal casing made in a series of disc-like members A each placed between ing a central hole atorn'iing a cell receiving; the central plate or diaphragm C of the dif ferential microphone and the microphone granules between which the plate (l lies.

other by he. thin insulating layers 1). The end walls of the diaphragm chamber or cell a are formed by the discs l3, the opposite faces oi which are recesscdto receive the carbon plates Z) which constitute the actual microphone walls. The central plates (l. two rl wlrich are shown but which may be of any convenient number, are connected rigidly together by the rod or stem (r which,

as shown in l igured, passes through the distance sleeve 0', which may he ofalumi'iu iuin. and projects at' one side for attachment to the light conical receiver diaphragm i i. if such diaphragm employed, or to anv other oscillating member, such as a member so niechanicall connected it a raniophone needle. The plates (1 need not be mounted one behind the other on a single rod, but ma be in parallel on branching rods so long as the connection between them ensures vibra- C vibrate in the same phase and any increase of pressure on the granules ell one side oi a plate is associated with a correspoiuling decrease of pressure on the granules at the other side, so that it the microphone is conn ected up in a difiercntial circuit, as for example the circuit shown in Figure 5, current Variations of considerable strength will be set up.

,rlhe discs A and l% are clamped together the screws F which extendcompletcly through the pile and are enclosed in insulating sheaths 7". The ring or frame (i carrying the diaphragm E is also secured to the casing by these screws. The light conical diaphrag'n'i is mounted in the ring G by the light flexible car clamping ring o. I

On the back plate B is mounted an insulating: block it carrying the four screw termiing ring 0 secured by the nuts 1'1 on the four metal plates 71. which are connected to the respectivctour dist B by .k'i'n'ows: iii one a! which is shown in F gure. 1,

a pair ol discs or plates 13, the discs A hav 50 and B a insulated from each 55 and fro movement while passing through the insulating sheath h and screwing into the second disc B. The central plates C are connected up to a separate lead so that the microphone circuit is completed through the plates C, the carbon granules in the cells a, the end plates b, discs B, terminals h and the externalleads and battery. The plates C may be supported in the cells by suitable soft insulating material lining the cell wall and permitting free to giving support. The two halves of the cells are divided by the plate G and the granules in the two halves kept separate. 4

' To fill the cellsa the discs A are made with the deep notches or recesses a at the upper side and small holes a? closed by plates a are provided at the bottom of the recesses a, leading into the cells a, as shown clearly in Figure 2. The plates a are removed to open the holes a and give access to the cells and when these are properly filled a packing of cotton wool or like material may be pushed into the holes a before replacing the plates a The microphone device shown is one particularly adapted for use with substantial current for loud speaking reproduction for 'gramophones or other instruments. The overheating of. the microphone has hitherto caused difficulties and has given rise to faulty and irregular transmission. In the present construction the mass of metal in direct contact with the microphones enables the heat to be conducted away rapidly and therefore avoids risk of overheating.

In Figure 5 a telephonic circuit is shown p which illustrates a special use of the differential microphones. The centre plates C are connected to one pole of a battery J while all the side plates are connected up in parallel to the other pole of the battery through the primaries 7c of the transformer K, the secondary coils 7c of the transformer being connected in series in the telephone receiver circuit L, a'receiver (or if preferred a telephone relay) being indicated at Z. More than one receiver or .relay Z may be included in the circuit. For loud reproduction of the sound loud speaking telephones may be employed, with megaphone trunr pets. The secondary coils 7c are as shown connected up alternately in opposition so as to compensate for any current changes which may be in the same direction in the primary coils, while the current changes due to the differential microphones are necessarily in opposite directionsin the two coils connected to the opposite plates. Thus no disturbances in the local battery circuit whi h are not due to the diit erential action of the microphones themselves would affect the secondary or receiver circuit.

Vl'here two or more microphones are used, a inv the diagram, the plates C are connectrea er? ed together as already described in order to vibrate in phase, but a single microphone may be employed with the transformer coils arranged to compensate each other.' The circuit shown is given merely as one ex ample of a compensating transformer and the differential microphone may, for example, be connected at its centre plate to the middle of a split battery to the poles of which the side plates are connected, the primary and secondary coils being so related as to give the required compensation in the secondary circuit.

In Figures 6, 7 and 8 an arrangement is illustrated diagrammatically by which a powerful reproduction is obtained at any distance, preferably by a set of loud speaking teiephoneswith trumpets arranged at suitable positions in a hall or room. The gramophone is provided with a corresponding set of differential microphones M each of which may be of the double or multiple differential microphone type already described with reference to Figures 1 to 4. These are placed across the end of the sound horn N on the end plate n which may close the end of the sound horn N completely or may have sound apertures (see Figure 8) n so that the gramophone can also be The horn N is arranged in any convenient manner in the casing, preferably tei minat ing at-the front as in the box horns commonly employed, passing from the tone arm 0 carrying the goose neck 0 and sound box 0 with needle 0 traversing the disc P. The sound produced in'the sound box 0' is transmitted through the horn N to all the microphones M, which are vibrated in phase with more evenly in a large room. -The connec-- tion between the microphones and receivers may be through a transformer arranged to compensate forexternal disturbances in the manner already described with reference to Figure 5.

l/Vhat I claim and desire to secure by Let tors Patent of the United States is 1. A microphone comprising in combination, a plurality'of substantial metal plates secured face to face, insulating material between said plates separating them from each other, one of said plates intermediate between the others having an aperture therein forming a llllCl'OPllOllG cell, a microphone plate supported in an insulated manner within said aperture, an external vibratory member, and means for connecting vibratory member to said microphone plate,

set forth.

2. A microphone comprising in combinadra -f tion, a plurality of substantial metal platessecured face to face, insulating material between said plate'sse arating them from each other, certain of sa'ic plates intermediate be- 5 tween the others having apertures therein forming microphonecells, a microphone plate supported in an insulated manner within each of said apertures, an external vibratory member common to all said micro phone plates, and means connecting said vibratory member to said microphone plates in such a manner that they vibrate in unison, as set forth. A microphone comprising in combination, a plurality of substantial metal plates secured face to face, insulating materialbe' tween said plates separating themfrom each other, one of said plates intermediate between the others having an aperture therein forming a microphone cell, aunicrophone 'plate supported in an insulated manner.

within said aperture, carbon discs mounted in recesses in the plates adjacent said intermediate plate forming the microphone walls, 5 an external vibratorymember, and means for connecting said vibratory member to said microphone plate, as set forth.

4. A microphone comprising in combination, a plurality of pairs of substantial metal plates having recesses therein, insulating material betweeneach pair of plates, a metal plate of larger dimensions than said recessed plates provided With an aperture and inserted between the two plates of each pair, insulating material separating -said larger'plates from said other plates, a microphone plate supported in an insulated manner within each of said apertures, an external vibratory member common to all said microphone plates, and means connecting 40 said vibratory members to said microphone plates in such a manner that they vibrate in unison, as set forth.

A microphone comprising a" massive metal casing built up of a series of substantial metal plates secured face to face,

a central aperture in an interior plate, forming a microphone cell,- a microphone plate supported in an insulated'manner withinthe said cell and between the ad jacentametal plates on each side, a deep channel in the said interior plate opening to the cell whereby .access is obtained to the cell for filling purposes and means for closing'the opening to the cell when the latter is filled.

6. A microphone comprising a massive metal casing built up of a series of substantial metal plates secured face to face, a central aperture in an interior plate, forming a microphone cell, a microphone plate supported in an insulated manner within the said cell and between the adjacent metal plates on each side, a deep channel in the saidinterior plate opening to the cell a erture, a passage leading from the channel into the cell aperture anda small covering plate for the said passage.

SIDNEY GEORGE BROWN. 

